CLS (Cumulative Layout Shift)
Checks Cumulative Layout Shift — how much the page jumps during load. Target under 0.1.
What this check measures
We query CrUX for p75 CLS. Target: under 0.1. Values over 0.25 fail. Usually caused by images without dimensions, late-loading fonts, or ads injected above content.
Why it matters
CLS means content jumping. Users click the wrong button mid-shift; that is a terrible experience and Google penalizes it. Easy to fix: explicit dimensions on every media element.
How our audit detects it
CrUX p75 CLS over 28 days. Lab CLS from PageSpeed as fallback.
Typical findings
- error_outlineImages without width/height attributes.
- error_outlineFont-display: swap causing text shift on font load.
- error_outlineCookie banner injected above fold after initial paint.
How to fix
Add width and height to every image, video, iframe. Use font-display: optional or preload critical fonts. Reserve space for cookie banners or ads with min-height.
Copy-paste fix prompt for your stack
Lovable · Cursor · Bolt · v0 · Replit · Windsurf · Claude Code · Base44
Frequently asked questions
How to fix font-swap CLS?expand_more
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Scan my siteRelated checks
LCP (Largest Contentful Paint)
Checks Largest Contentful Paint — how fast the main content appears. Target under 2.5s.
PerformanceINP (Interaction to Next Paint)
Checks Interaction to Next Paint — responsiveness to clicks/taps. Target under 200ms.
PerformanceFCP (First Contentful Paint)
Checks First Contentful Paint — when the first text or image appears. Target under 1.8s.
PerformanceTTFB (Time to First Byte)
Checks Time To First Byte — server response time. Target under 600ms.